For decades, the word rapist has conjured up the image of a stranger lurking in the shadows.

But today, a rapist could be standing next to you in the pub, having a friendly chat, buying you a drink.

Reported cases of date rape - a sexual attack by a friend, a colleague, or love interest - are on the increase.

And many of these sexual predators are armed with easily administered drugs such as Rohypnol or GHB (gamma-hydroxybutate) to sedate their victims into pliant submission.

Date rape drugs

GHB - colourless, odourless, slightly salty taste

Rohypnol - tasteless and odourless

Victims lose memory and inhibitions, become open to suggestion

Since November 1997, more than 2,900 people - including 246 men - have contacted the Roofie Foundation, a helpline for date rape victims.

"Using a drug makes it easier, whether or not you know the victim," says the foundation's chief executive Grahams Rhodes. "Many of the victims, to this day, don't really know what happened to them."

Mr Rhodes says it is alarming how easy it would be for a would-be rapist to drop a sedative into an unattended drink.

"You go into any pub, in any town, between 6pm and 8pm, and say to yourself: 'How many drinks could I spike?' People leave drinks all over the place."

Misplaced trust

The evening nursing sister Susan Annis died at the hands of a would-be rapist started out innocently enough. She met a colleague, Kevin Cobb, for a drink, a bite to eat, a bit of a laugh.

Kevin Cobb denies drugging his victims

But that night in November 1996 ended in tragedy. After drinking a cider laced with the sedative Midazolam, she stopped breathing because her mild heart condition caused an adverse reaction to the drug.

A jury at London's Old Bailey found Cobb guilty of the manslaughter of Ms Annis and other counts of drug rape.

There have been a number of high-profile cases where the victim, knowing their attacker, was lulled into a false sense of security. Sometimes they were drugged, sometimes they trusted - and maybe were attracted to - the rapist.

Boxing champion Mike Tyson served three years of his sentence for raping beauty contestant Desiree Washington in an Indianapolis hotel room in 1991.

Mike Tyson invited Desiree Washington to his hotel room

He denied harming the 18-year-old because, he said, her eyes were not blackened and no ribs were broken.

In 1993, solicitor Angus Diggle, 35, was given a three-year sentence for the attempted rape of a woman solicitor after a ball.

Her friends found him wearing only frilly cuffs and a luminous condom. He told police: "I spent £200 on her. Why can't I do what I did to her?"

Advice for drug rape victims

Report attack asap - drugs leave the body within four days

Refuse sedatives - these can mask drugs in tests

Write down details as they come back

Tyson and Diggle did not drug their victims, nor did an Israeli travel agent who was convicted last year for the kidnap and rape of the 1998 Miss World, Linor Abargil.

Shlomo Uri Noor had offered to drive the beauty queen home from Italy to Israel. She said he raped her at knifepoint during the trip.

Last October, Welsh brothers Graham and Simon Laskey were jailed for life for drug raping women they contacted through lonely-hearts advertisements over an 18-year period.

Blue dye in Rohypnol shows up after 20 minutes

In a review of the Sex Offences Act due out next month, the Home Office has been considering whether to impose lesser sentences for date rape. The review team is widely expected to reject this option.

The legal status of the so-called date rape drugs is also under review, and Rohypnol and GHB could be banned.

Rohypnol, a powerful sedative known as roofie or the forget-me-pill, is banned without a prescription in the UK and the United States.

In February, the US President Bill Clinton also banned GHB. Yet the drug is available over the counter in the UK for easing sleep disorders. Also called GBH and liquid ecstasy, it is the current drug of choice among nightclubbers.

"Those two [drugs] are the main offenders," Mr Rhodes says.

"The one [Cobb] used is not on the streets - Midazolam is a hospital-only drug. We don't think this one is going to take off."